Immune mechanisms may be involved in the pathogenesis of idiopathic progressive bilateral sensorineural hearing loss (IPBSNHL). Uncontrolled studies suggest that corticosteroids treatment reverses the hearing loss of some patients. Specific cellular and humoral immune responses have been detected in some patients, but serologic markers that might identify patients likely to respond to treatment, have not been established. Our prior studies suggested that corticosteroid treatment is effective in some patients with IPBSNHL and that the presence of antibody to inner ear antigens and to type II collagen correlate with steroid responsiveness. The proposed study seeks to determine the efficacy of corticosteroid treatment of IPBSNHL utilizing a prospective, double-masked, randomized, placebo-controlled trial. The diagnostic and prognostic value of certain immunologic assays, as well as their ability to predict steroid responsiveness will be determined. Serum antibodies reactive with inner ear antigens will be assayed using Western blot and indirect immunofluorescence techniques. Serum antibodies reactive with type II collagen will be measured using an enzyme-linked immunoassay. The proliferative response of peripheral blood mononuclear cells to inner ear antigen will be determined. Activated T lymphocytes will be identified using monoclonal antibodies to stable T cell markers and to activation antigens; doubly stained cells will be enumerated by flow cytometry. The detection of activated T cells may be correlated with steroid-responsiveness and may help to identify patients who are, or are not, likely to benefit from treatment. The clinical course, laboratory findings, and repsonse to treatment of patients in this study may help to determine whether IPBSNHL is a single distinct entity or whether one or more subsets of patients with SNHL can be identified.